TEM investigation of the oxide scale of Ti-46.5Al-5Nb at 900 °C for 50 h

In the present work, microstructure of oxide scale of Ti-46.5Al-5Nb oxidized for 50 h at 900 °C in air was investigated in both plane-viewed and cross-sectional samples using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). In the TiO2 and Al2O3 mixture layer, orientation relationships (OR) between the Al2O3 and TiO2 phases were identified to be [11¯0]Al2O3//[001]TiO2 and (001)Al2O3//(110)TiO2, however, some misorientation existed at their interface. Besides, Nb enrichment was detected in the TiO2 phase in this layer but no Nb was found in the outer TiO2 layer. Al3Nb phase was identified between the oxide scale and TiAl base. This phase would promote TiAl oxidation protection due to hinder 'x' phase continuous formation.